This invention relates to a weighing system, and more particularly, to a system that determines the gross weight and center of gravity (CG) of an object.
Most of the time consumed in weighing system routine maintenance is devoted to calibrating the strain-gauge type load cells used in prior art systems. As a load cell ages, its nonlinearity also increases. Prior art systems require load cell linearity of better than 0.05% of full scale to ensure an accurate answer. They use alternating current to power the load cells. Although this simplifies the detection circuitry design, the reading is affected by the cable capacitance. This in turn requires that the entire weighing system has to be returned to the shop as a whole for calibration, which is very inconvenient.
The cells in prior art systems, in addition, are generally excited one at a time during operation as there is only one detection circuit which is manually switched to read the selected cell. Since a cell requires a 30-minute stabilization period under power to balance internal self heating effects, a precision weighing routine for a system with four load cells will take at least two hours.
Gross weight and center of gravity are very important values, in particular for aircraft applications, since they allow for fast pre-flight trimming of an aircraft's weight. Because only one cell can be read at a time, prior art systems are unable to provide automatic calculation of these values; manual calculation is necessary.
Also, the prior art systems are generally based on a technology at least 10 years old. This technology does not contemplate self-diagnostic routines for verifying the system operating condition.
Therefore, it is an object of this invention to provide a weighing system that automatically determines the center of gravity and gross weight.
Another object of this invention is to provide a weighing system capable of providing highly accurate results even with highly nonlinear load cells.
A further object of this invention is to provide a weighing system whose operating condition can be easily verified and manipulated by any operator.
Still another object of this invention is to provide a weighing system capable of determining weight either with stored memory data or manually keyed data.